1. Field of the Invention
It is well known that automobiles typically utilize what is commonly referred to as four cycle internal combustion engines wherein each moving compression element travels repeatedly through four strokes, designated as intake, compression, power and exhaust. The compression element is typically a piston which reciprocates within a cylinder, but may vary in configuration such as in a Wankel type engine wherein the compression element is a specially configured rotor.
It is also well known that the proper timing of the ignition spark is critical for optimum performance of such internal combustion engines which are based on an ignition spark for igniting the fuel-air mixture. Experience has shown that optimum engine performance is achieved when the spark which triggers ignition occurs before the piston reaches the top dead center (TDC) position of its travel, as it completes the compression stroke. When an ignition spark precedes the piston reaching TDC, this is commonly referred to as timing advance. In modern engines complex mechanical devices and elaborate electronic and computerized systems have been utilized to adjust the timing in response to various criteria. Engine speed is the most critical criteria requiring changes in timing advance and is also the criteria requiring the greatest change in timing advance. To a lesser degree other criteria must also be considered. These include parameters such as engine load, engine temperature, quality of fuel, fuel-air ratio, ambient conditions, emission control requirements, etc. In the light of these requirements, the present invention relates to a system which provides a simple and inexpensive electronic means for precise control of the ignition timing advance in internal combustion engines. This system is based on the measurement and comparison of time elapsed between consecutive TDC piston positions, and the addition of an appropriate time value.
2. Description of Related Art
Heretofore one typical means for advancing ignition timing in relation to engine speed is commonly referred to as a centrifugal advance system, wherein the shaft of an ignition distributor is provided with two or more weights which are biased by springs. As the speed of the distributor shaft increases the weights are forced outwardly against the bias of the springs, and through a mechanical linkage the ignition timing is advanced as the rotational speed of the distributor shaft increases. These weights, springs and mechanical linkages must be manufactured with precision and must be carefully calibrated. Because of mechanical friction, changing spring constants and engine speed variations, this system is not completely accurate in principle and becomes less so after use. For example, as a result of wear, friction increases in the mechanical parts; and with normal use and exposure to extreme temperatures, the elastic constants of the springs change from original design specifications. Also, servo mechanical or electronic systems require an input which is sensed before correction of the input is introduced. This results in a "searching" action which is repeated until the optimum condition is reached. Mechanical servo systems are also unstable because of inertial effects. Accordingly, it will be readily appreciated that systems of this type are basically lacking in accuracy over large ranges of engine speed and extended use, are very expensive to manufacture, and require costly periodic maintenance.
A more recent development for improving the ignition timing accuracy is the computer controlled system. In these systems the computer receives synchronization pulses from the distributor's pick-up coil, computes the engine speed and by utilizing special programming and tables, computes an the optimum advance angle from inputs relating to engine performance parameters. Such systems are typically quite accurate, but involve complicated electronic equipment, expensive parts and sensors. Custom programming and careful studies of the optimum angle for each application of the computer tables and programs is also required. Typically, if a system of this type fails, the original program and tables must be replaced, because they are not interchangeable between models. Also, later adjustments to the ignition timing are not possible without reprogramming. Replacement of expensive computer parts may also be required. Further, the accuracy of this method is only as good as the initial program and tables. Original accuracy can be substantially degraded if fuels having widely varying characteristics are used or if the automobile is driven at speeds, altitudes or temperatures outside those for which the computer was initially programmed. Typically, in such computer systems, a fixed angle of advance is built into the distributor position for use in the event a computer malfunction makes it necessary to eliminate the computer and operate in a so-called "limp mode".
Examples of related prior art are found in the following U.S. Patents: U.S. Pat. No. 3,888,220 to Bigalke et al. which relates to performance curve control of the ignition angle advance in an internal combustion engine; U.S. Pat. No. 4,122,807 to Hosaka et al. which utilizes a reference angle signal generator to detect the angular position of a crankshaft and in response thereto generates reference angle signals corresponding to the reference angle positions such as top dead center piston positions. The patent utilizes divided signals to produce ignition spark triggering signals conforming to advance control signals applied as inputs thereto; U.S. Pat. No. 4,138,976 to Crall which utilizes a pair of magnetic pickup devices, each of which generates signals at a frequency representative of engine speed; U.S. Pat. No. 4,852,536 to Maier et al. which utilizes a computing means which controls the sparks to a plurality of cylinders, and is based upon the identification of the timing of cylinder number one; U.S. Pat. No. 4,917,064 to Kodoma et al. which is directed primarily to a cylinder discriminating reluctor; U.S. Pat. No. 4,959,996 to Akasu which uses a shortened output pulse of a prescribed reference cylinder of the engine, for comparison to the longer pulses generated by the remaining cylinders, and utilizes the period between consecutive output pulses in conjunction with a ratio calculator and other electronic components to control the ignition advance angle of an engine; U.S. Pat. No. 5,046,468 to Erhard which utilizes tangentially adjacent tooth segments as inductive pickup devices; and U.S. Pat. No. 5,056,485 to Kobayashi et al. which provides a rotor plate formed with slits for detecting angular cylinder position.
It is apparent that none of the above referenced patents suggests a system similar to that of applicant nor do they overcome the shortcomings of the prior art with a simple and inexpensive system, which is disclosed in detail hereinafter.